In recent years, the transition to full IP/Ethernet based backbone networks has been developed in telecommunications carriers. This results in a situation where backbone networks based on the existing SDH/SONET technology and backbone networks based on the new IP/Ethernet technology exist together.
Under such circumstances, in order to eliminate inefficiency in the equipment and maintenance due to the coexistence of networks, a study has been made on the aggregation of SDH/SONET signals into IP/Ethernet-based backbone networks by converting the signals into IP/Ethernet packets. More specifically, the study involves T-MPLS technologies defined in ITU-T Y.1370.1, Y.1371, Y. 1381, and the like.
However, lower-order paths such as VC-11 and VC-12 defined in ITU-T G.707, which is the standard of SDH, are configured with the number of bytes per path in one frame as only 27 bytes (25 bytes for the true user traffic part, excluding management bytes) and 36 bytes, respectively. Thus, in the case of the lower-order path, the ratio of the non-payload occupying in communication increases due to the overhead added in packetization, as well as the gap between frames, depending on the unit of performing the packetization. On the other hand, the ratio of the payload decreases. In order to prevent this, there can be considered a method, as described in non-patent document 1, in which a lower-order path is once accumulated for a sufficiently long time based on the unit of frame, and the accumulated data are packetized all at once. For example, when a path of VC-11 is accumulated for 10 frames of STM-0, the ratio of the payload can be increased to 10 times. Non-patent document 1 recommends a method of accumulating a lower-order path for an integer multiple of bytes, with 25 bytes as the base unit (for one frame), and packetizing the accumulated bytes all at once. However, as the accumulation time becomes longer, the delay time naturally increases.    Non-patent document 1: ITU, “ITU-T Y.1413 TDM-MPLS network interworking-User plane interworking”, Section 9.1.1. 2004